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Old 11th December 2010, 07:24 AM   #1
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Default Replacing broken volume control with digital volume control

Hi all,
I have multichannel solid state amplifier, but the right channel volume control (potentiometer) was broken.

I can not find the part for replacement, so I want to replace it with digital volume control.

My plan is using the left channel potentiometer as a control for new digital stereo volume control.

Please help me, I need circuit diagram for this,

thankyou in advance.
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Old 11th December 2010, 07:35 AM   #2
Mooly is offline Mooly  United Kingdom
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Using a pot to control a digital attenuator is far from easy, I don't know how you would do it without purpose writen code to interface it to a "one off" purpose built attenuator...

You could use it to control an analogue VCA (voltage controlled amplifier) though, but surely fitting a conventional replacement pot is far far easier.
Digital control usually requires either a rotary encoder for control or up/down buttons. All the original pot can do is generate a variable resistance (or voltage) and nothing more. What happens if the good side of the pot goes faulty?

Is the original motorised ? Photos ? Make model etc ?
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Old 11th December 2010, 05:03 PM   #3
banana is offline banana  Hong Kong
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I agree with Mooly, it will be difficult to use a volume pot to control digital attenuator. I have made it by feeding the pot with 5Vdc, and then encode the pot voltage by an ADC. The whole thing is quite clumsy. See link below.

Banana's Pre - inelegant way to contrl vol
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Old 12th December 2010, 05:11 AM   #4
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Thank's Guys,
I searched the net, and I find more simple solution using optocoupler like this:
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

what do you think?
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Old 12th December 2010, 06:07 AM   #5
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Gunawan W View Post
Thank's Guys,
I searched the net, and I find more simple solution using optocoupler like this:
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

what do you think?
It needs a dual pot... and yours is broken
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Old 12th December 2010, 07:38 AM   #6
h_a is offline h_a  Europe
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Quote:
All the original pot can do is generate a variable resistance (or voltage) and nothing more.
No problem with that, use ADC to get the position/direction.

But, of course, I agree with Mooly, it's a not so easy task, even more so for commercial multichannel amp with little space left.
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Old 12th December 2010, 12:26 PM   #7
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How about this schematic? it use single pot....

diyparadise - all about volume control...
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Old 12th December 2010, 04:33 PM   #8
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Gunawan W View Post
How about this schematic? it use single pot....

diyparadise - all about volume control...
Who are you trying to convince...

How much current is going to flow via the pot wiper at the end of it's travel. I'll let you worki it out... I wouldn't count on the remaining good side of your pot staying good for very long though
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Old 13th December 2010, 02:06 AM   #9
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Hi Mooly,
I don't know how much current...
I only knew that the right channel was broken, maybe it was because my daughter turn it at max at one time when I turn it it on... the amp is 100 watt per channel.

thank's
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Old 13th December 2010, 06:28 AM   #10
Mooly is offline Mooly  United Kingdom
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The current is just ohms law.
A 5 volt supply
A resistor to limit current (stated as 24 to 100ohm)
The volt drop across the LED... say 2 volts.

So we 5-2 =3volts.
3 volts across 24 ohm is 0.125amp. As the pot is turned from zero resistance that current will burn the resistive track at the ends.

Why can you not just fit a normal pot... what's the problem. Must be far easier than all this.
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